C# comboBox实现省市两级联动（winform）

新建一个win form应用程序，拖两comboBox控件。数据库见前一篇文章。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace 省市
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            using (SqlConnection conn = new SqlConnection("server=.;database=DBPromary;user id=sa;password=123456"))
            {
                conn.Open();

                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = "select proName from promary";

                    using (SqlDataReader reader = cmd.ExecuteReader())
                    {

                        while (reader.Read())
                        {
                            string name = reader.GetString(reader.GetOrdinal("proName"));
                           
                            cb1.Items.Add(name);
                        }
                    }
                }
            }

        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            cb2.Items.Clear();
            using (SqlConnection conn = new SqlConnection("server=.;database=DBPromary;user id=sa;password=123456"))
            {
                conn.Open();

                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = "select cityName from city,promary where city.proID=promary.proID and promary.proName=@pname";
                    cmd.Parameters.Add(new SqlParameter("pname",cb1.SelectedItem));

                    using (SqlDataReader reader = cmd.ExecuteReader())
                    {

                        while (reader.Read())
                        {
                            string name = reader.GetString(reader.GetOrdinal("cityName"));

                            cb2.Items.Add(name);
                        }
                    }
                }
            }

        }
           
           
        }
    }